SGER: A Difference Frequency Generation Microscope

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The Analytical and Surface Chemistry program in the Division of Chemistry will support the research program of Prof. Heather Allen of Ohio State University through a small grant for exploratory research (SGER). The goal of this work is to develop a new method with the capability to image liquid surfaces using vibrational second-order spectroscopy. While infrared and Raman microscopy are well utilized tools for imaging films on solid surfaces, nonlinear techniques using vibrational difference-frequency (or sum-frequency) microscopy provides markedly greater sensitivity for imaging the air-liquid interface. Currently, sum frequency spectroscopy is used to obtain spectra from liquid surfaces; however, sum-frequency imaging is far from being commonplace mainly because of technical complexity. Prof. Allen and her students will utilize infrared microscope technology an optical platform for the design of a difference-frequency microscope. The hypothesis to be tested in this high risk high impact study is that combining a high repetition rate red laser with a continuous wave infrared source, will generate a small number of difference-frequency photons that could be imaged with careful optimization of detection variables. Alternatively, utilizing a high repetition rate infrared source combined with red laser pulses will provide a large number of photons that can more easily be imaged using the infrared microscope platform. This molecularly selective and highly sensitive difference-frequency microscope will have application to imaging in biology, materials, and environmental and atmospheric aerosol research.